class Stack(object):
    def _init_(self,limit=10):
        self.stack = []
        self.limit = limit
    def is_empty(self):
        return len(self.stack) == 0
    def push(self,data):
        if len(self.stack) >= self.limit:
            print("栈溢出")
        else:
            self.stack.append(data)
        def pop(self):
            if self.stack:
                return self.stack.pop()
            else:
                print("空栈不能被弹出")
        def top(self):
            if self.stack:
                return self.stack[-1]
        def size(self):
            return len(self.stack)
stack=Stack
print(stack.size())
stack.push(1)
stack.push(2)
stack.push(3)
stack.push(4)
print(stack.size())
print(stack.is_empty())
print(stack.top())
print(stack.pop())
print(stack.top())

